[00:00.00]NARRATOR: Listen to part of a lecture in a Biology class.
[00:03.94]FEMALE PROFESSOR: OK, for today, let's look at a reptile—a predator—that hasn't evolved much in the last 70 million years. [00:15.61]No discussion of reptiles would be complete without some mention of crocodiles.[00:20.64]Now, we tend to think of crocodiles as uh, kind of solitary...hiding out in a swamp, kind of mysterious creatures... [00:29.75]But we're finding out that they aren't as isolated as they seem. [00:33.61]In fact, crocodiles interact with each other in a variety of ways. [00:38.04]One way is with vocalizations...ya know, sounds generated by the animal. [00:43.15]This is true of the whole crocodile family which includes crocodiles themselves, alligators, etc...
[00:50.09]Take American alligators. [00:52.59]If you were to go to a swamp during the breeding season, you'd hear a chorus of sounds. Deep grunts, hisses...These are sounds that male alligators make, [01:03.29]and some of them are powerful enough to make the water vibrate. [01:06.45]This sends a strong "go away" message to the other males, [01:11.01]so the alligator can focus on sending other sound waves through the water...sound waves that you and I couldn't even hear since they're such low frequency. [01:19.65]But they do reach the female alligator, who then goes to find, and mate with, the male.
[01:25.56]Vocalization is, um, well, it's used for other reasons...like getting attention or dis—ah, letting others know that you're distressed. [01:35.29]Ah, let's see...[01:36.55]newborn crocodiles, or hatchlings, and their interactions with their mother. [01:40.61]When they're born, croc- baby crocodiles have a sort of muffled cry while they're in their nest. [01:47.49]Hatchlings are really vulnerable—especially to birds and small mammals—when they're born, [01:53.35]but their mother, who's been keeping vigil nearby, hears their cry for help and carries them to safety...meaning, to water.
[02:01.23] So, she takes them out of the nest,ah, [02:03.89]um, all the eggs hatch at once, so she has about 40 newborns to look after. [02:10.00]She takes about 15 out of the nest at a time, carrying them in her mouth to the nearby water. [02:16.35]While she's taking one load of hatchlings, the others wait for her to come back, [02:21.24]but do you think they're quiet about it? No way! [02:24.72]They're clamoring for the mother's attention, sort of squeaking, and practically saying, "Don't forget about me!"
[02:30.62] I heard some great examples of this on a television program on crocodiles last week...[02:35.28]anyone catch it? [02:36.46]It had a few interesting bits, [02:38.41]but you know...[concerned] uh, you have to be careful, think critically. [02:42.87]Sometimes I don't know where these shows find their "experts."
[02:50.43]MALE STUDENT: Excuse me. [02:53.59]But um, does all that crying defeat the purpose? [02:56.36] I mean, doesn't it...attract more predators?[02:59.06]FEMALE PROFESSOR: Hmm, good question. [03:01.41]I guess—well, I'm guessing that once the babies have the mother's attention, they're safe. [03:07.28]She's never too far away, an-and I think—I mean, would you mess with a mother crocodile?[03:17.56]So, after the mother transports all the youngsters, they still call to each other, and to their mother. [03:26.44]This communication continues right through to adulthood. [03:29.89]Crocodiles have about 18 different sounds that they can make.
[03:33.60] There's—uh, uh, you have deep grunting sounds, hisses, growls, squeaks, roars...So, there are many different sounds to interact or send messages. [03:45.91]This is more typical of mammals than of reptiles...[03:49.24]I mean, crocodiles' brains are the most developed of any reptile...[03:52.70]in that sense, they're closer to mammals' brains than other reptiles' brains. [03:56.79]And we know that mammals...ah, well dogs, for example...dogs vocalize many different sounds. [04:03.46]Crocodiles have a similar level of, ah, vocal sophistication, if you will—which makes them unique among reptiles.
[04:11.94]Another thing would be, ah, if a hatchling gets separated from the rest of its family. Once the others get far enough away, its survival instinct kicks in. [04:22.28]It'll make a loud distress call, which its siblings answer...[04:26.19] it calls again, [04:27.59]and they continue calling back and forth until they all find each other again.[04:31.49]Another thing, something that wasn't on that TV show I mentioned—[04:35.85]ah, mother crocodiles lead their young from one area to another, like when they have to find a different source of water. [04:43.69]Usually she'll lead them at night, when it's safer for them, moving ahead and then letting out calls of reassurance so that they'll follow her. [04:51.69] Her voice helps give the babies the courage they need to leave the area and go someplace that's a more desirable home for them.
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